Posted on by

Electronic Control System Gas Plus Engines – FAULT CODE 1129 – B and C Gas Plus

Humidity Sensor – Voltage Below Normal

Overview

CODE REASON EFFECT
Fault Code: 1129
PID: 370
SPN: 2946
FMI: 4
LAMP: Amber
SRT: 

Humidity Sensor – Voltage below normal or shorted to a low source. Low signal voltage detected at the humidity sensor signal circuit at the ECM.

Possible reduced performance.

Humidity Sensor Circuit
SMALL | MEDIUM | LARGE

Circuit Description

The electronic control module (ECM) uses the humidity sensor to measure relative humidity. The humidity sensor is connected to sensor supply number 1.

Component Location

The humidity sensor is located in the mixer inlet elbow near the fuel housing.

Shop Talk

Relative humidity is calculated using the intake manifold temperature sensor, intake manifold pressure sensor, and humidity sensor. The units are displayed in grains/pound mass of dry air. The humidity sensor can only provide a valid reading under certain engine operating conditions. The value displayed for specific humidity is the last value updated by the sensor. A value of 75 grains is the default and will be displayed until the engine operating conditions are met for an update.

Cautions and Warnings

 CAUTION 

To reduce the possibility of damaging a new ECM, all other active fault codes must be investigated prior to replacing the ECM.
 CAUTION 

To reduce the possibility of pin and harness damage, use the following test leads when taking a measurement:
Part Number 3164596 – male Framatome test lead

Troubleshooting Steps

STEPS SPECIFICATIONS
STEP 1. Check the fault codes.  
  STEP 1A. Check for sensor supply fault codes. Fault Code 352 or 386 active?
  STEP 1B. Read the fault codes. Fault Code 1129 active?
STEP 2. Check the humidity sensor and circuit.  
  STEP 2A. Inspect the humidity sensor and connector pins. Dirty or damaged pins?
  STEP 2B. Check the sensor supply voltage and return circuit. 4.5 to 5.3 VDC?
  STEP 2C. Check the circuit response. Fault Code 1128 active and Fault Code 1129 inactive?
  STEP 2D. Check the fault codes and verify sensor condition. Fault Code 1129 active?
STEP 3. Check the ECM and engine harness.  
  STEP 3A. Inspect the ECM and engine harness connector pins. Dirty or damaged pins?
  STEP 3B. Check for an open circuit in the engine harness. Less than 10 ohms?
  STEP 3C. Check for an open circuit in the engine harness. Less than 10 ohms?
  STEP 3D. Check for a pin-to-pin short circuit in the engine harness. Greater than 100k ohms?
  STEP 3E. Check for a pin short circuit to ground. Greater than 100k ohms?
  STEP 3F. Check for an inactive fault code. Fault Code 1129 inactive?
STEP 4. Clear the fault codes.  
  STEP 4A. Disable the fault code. Fault Code 1129 inactive?
  STEP 4B. Clear the inactive fault codes. All fault codes cleared?

Guided Step 1 – Check the fault codes.

Guided Step 1A – Check for sensor supply fault codes.

Conditions

  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

  • Use INSITE™ electronic service tool to read the fault codes.

Fault Codes 352 and/or 386 active?
YES NO
No Repair No Repair
Fault Code 352 and/or 386

Guided Step 1B – Check the fault codes.

Conditions

  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

  • Use INSITE™ electronic service tool to read the fault codes.

Fault Code 1129 active?
YES NO
No Repair No Repair

Procedure 019-361

Guided Step 2 – Check the humidity sensor and circuit.

Guided Step 2A – Inspect the humidity sensor and connector pins.

Conditions

  • Turn keyswitch OFF
  • Disconnect the humidity sensor from the engine harness.

Action

  • Corroded pins
  • Bent or broken pins
  • Pushed back or expanded pins
  • Wire insulation damaged
  • Moisture in or on the connector
  • Missing or damaged connector seals
  • Connector shell broken
  • Dirt or debris in or on the connector pins.

For general inspection techniques, refer to Component Connector and Pin Inspection, Procedure 019-361.

Dirty or damaged pins?
YES NO

A defective connection has been detected in the sensor or harness connector.

Clean the connector and pins.

Repair the damaged harness, connector, or pins if possible.

Refer to Procedure 019-043

Refer to Procedure 019-218.

Refer to Procedure 019-356.

 No Repair

Guided Step 2B – Check the sensor supply voltage and return circuit.

Conditions

  • Turn keyswitch OFF
  • Disconnect the humidity sensor from the engine harness
  • Turn keyswitch ON.

Action

  • Measure the voltage between the humidity SUPPLY pin and the humidity RETURN pin at the humidity sensor connector of the engine harness.

Refer to the circuit diagram or wiring diagram for connector pin identification.

4.5 to 5.3 VDC?
YES NO
No Repair No Repair

Guided Step 2C – Check the circuit response.

Conditions

  • Turn keyswitch OFF
  • Disconnect the humidity sensor from the engine harness
  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

  • Check for the appropriate circuit response after 30 seconds.
  • Use INSITE™ electronic service tool to read the fault codes.

Fault Code 1128 active and Fault Code 1129 inactive?
YES NO
No Repair No Repair

Guided Step 2D – Check the fault codes and verify sensor condition.

Conditions

  • Turn keyswitch OFF
  • Connect the humidity sensor to the engine harness
  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

  • Use INSITE™ electronic service tool to read the fault codes.

Fault Code 1129 active?
YES NO

A defective sensor has been detected.

Replace the humidity sensor.

Refer to procedure 019-356.

None. The removal and installation of the connector corrected the failure.

Guided Step 3 – Check the ECM and engine harness.

Guided Step 3A – Inspect ECM and engine harness connector pins.

Conditions

  • Turn keyswitch OFF
  • Disconnect the engine harness connector 1 from the ECM.

Action

  • Corroded pins
  • Bent or broken pins
  • Pushed back or expanded pins
  • Wire insulation damaged
  • Moisture in or on the connector
  • Missing or damaged connector seals
  • Connector shell broken
  • Dirt or debris in or on the connector pins.

For general inspection techniques, refer to Component Connector and Pin Inspection, Procedure 019-361.

Dirty or damaged pins?
YES NO

A defective connection has been detected in the ECM or engine harness connector.

Clean the connector and pins.

Repair the damaged harness, connector or pins if possible.

Refer to Procedure 019-043.

Refer to Procedure 019-204.

Refer to Procedure 019-031.

 No Repair

Guided Step 3B – Check for an open circuit in the engine harness.

Conditions

  • Turn keyswitch OFF
  • Disconnect the engine harness connector 1 from the ECM
  • Disconnect the humidity sensor from the engine harness.

Action

  • Measure the resistance between the engine harness ECM engine connector 1 humidity SUPPLY pin and the engine harness humidity sensor connector SUPPLY pin.

Refer to the circuit diagram or wiring diagram for connector pin identification.

For general resistance measurement techniques, refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360.

Less than 10 ohms?
YES NO
No Repair

An open supply circuit has been detected in the engine harness.

Repair or replace the engine harness.

Refer to Procedure 019-204.

Refer to Procedure 019-043.

Guided Step 3C – Check for an open circuit in the engine harness.

Conditions

  • Turn keyswitch OFF
  • Disconnect the engine harness connector 1 from the ECM
  • Disconnect the humidity sensor from the engine harness.

Action

  • Measure the resistance between the engine harness ECM engine connector 1 humidity SIGNAL pin and the engine harness humidity sensor connector SIGNAL pin.

Refer to the circuit diagram or wiring diagram for connector pin identification.

For general resistance measurement techniques, refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360.

Less than 10 ohms?
YES NO
No Repair

An open signal circuit has been detected in the engine harness.

Repair or replace the engine harness.

Refer to Procedure 019-204.

Refer to Procedure 019-043.

Guided Step 3D – Check for a pin-to-pin short in the engine harness.

Conditions

  • Turn keyswitch OFF
  • Disconnect the engine harness connectors 1 and 2 from the ECM
  • Disconnect the humidity sensor from the engine harness.

Action

  • Measure the resistance between the humidity SIGNAL pin in the engine harness ECM engine connector 1 and all other pins in the engine harness connector 1.
  • Measure the resistance between the humidity SIGNAL pin in the engine harness ECM engine connector 1 and all other pins in the engine harness connector 2.

Refer to the circuit diagram or wiring diagram for connector pin identification.

For general resistance measurement techniques, refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360.

Greater than 100K ohms?
YES NO
No Repair

A pin-to-pin short circuit on the signal line has been detected in the engine harness.

Repair or replace the engine harness.

Refer to Procedure 019-204.

Refer to Procedure 019-043.

Guided Step 3E – Check for a pin short circuit to ground.

Conditions

  • Turn keyswitch OFF
  • Disconnect the engine harness connector 1 from the ECM
  • Disconnect the humidity sensor from the engine harness.

Action

  • Measure the resistance between the humidity SIGNAL pin in the engine harness ECM engine connector 1 and engine block ground

Refer to the circuit diagram or wiring diagram for connector pin identification.

For general resistance measurement techniques, refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360.

Greater than 100K ohms?
YES NO
No Repair

A pin to ground short circuit on the signal line has been detected in the engine harness.

Repair or replace the engine harness.

Refer to Procedure 019-204.

Refer to Procedure 019-043.

Guided Step 3F – Check for an inactive fault code.

Conditions

  • Connect all components
  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

  • Use INSITE™ electronic service tool to read the fault codes.

Fault Code 1129 inactive?
YES NO

None. The removal and installation of the connector corrected the failure.

Call for pre-authorization.

Replace the ECM. Refer to Procedure 019-031.

Guided Step 4 – Clear the fault codes.

Guided Step 4A – Disable the fault code.

Conditions

  • Connect all components
  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

  • Start the engine and let it idle for one minute.
  • Use INSITE™ electronic service tool to verify the fault code is inactive.

Fault Code 1129 inactive?
YES NO
No Repair

Troubleshooting procedures need to be repeated from the beginning.

Guided Step 4B – Clear the inactive fault codes.

Conditions

  • Connect all components
  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

  • Use INSITE™ electronic service tool to erase the inactive fault codes.

All fault codes cleared?
YES NO
No Repair

Troubleshoot any remaining active fault codes.
Repair complete
Appropriate troubleshooting steps
Last Modified:  22-Sep-2004
Avatar photo

Published by Jack

Hello, I'm Jack, a diesel engine fan and a blogger. I write about how to fix and improve diesel engines, from cars to trucks to generators. I also review the newest models and innovations in the diesel market. If you are interested in learning more about diesel engines, check out my blog and leave your feedback.